A chuck for rotary tools in prior art, for example a drill chuck, generally includes a chuck body, a jaw, a nut, a bearing, an anti-loosening unit and an outer sleeve, wherein the chuck body is connected to a transmission spindle of a driving device, three jaws are respectively mounted in three inclined holes equally arranged in the chuck body, the jaw is provided with thread to form thread transmission together with the nut. When the outer sleeve connected to the nut is rotated, the jaws can be moved with respect to the chuck body so as to grip or release a tool handle.
In the above structure, due to the large contact stress produced by the thread between the jaws and the nut under operating load, the friction force of relative sliding therebetween is great. As a result, the gripping force to grip a tool handle, produced by the thread transmission between the nut and the jaws, tends not to be great enough, such that the jaws can not grip stably the tool handle under the operating condition of great load and vibration. In addition, several disclosed anti-loosening structures are not effective in anti-loosening owing to the limits in their structures, for example, the structure in PCT/CN02/00375 has problems such as loosening under the operating condition of vibration and impact.
Aiming to improve the locking performance of a chuck and prevent jaws from loosening in operation, many chucks with anti-loosening function have been developed, for example, a chuck for rotary tools is disclosed in U.S. Pat. No. 5,031,925. The chuck comprises a chuck body, a rear cap, three jaws, an outer sleeve, a pawl seat, a pawl and a control member, wherein the rear end of the chuck body is connected to a transmission shaft of a driving device. The rear cap is fixedly provided on the rear end of said chuck body. The outer sleeve is rotatablely fitted around the chuck body and located in front of the rear cap. The inner side of the outer sleeve is connected with the control member and drives it. The control member presses down the rear end of the pawl member such that the pawls on the front end of the pawl member are disengaged from the ratchets provided on the chuck body. In such a chuck, the pawls of the pawl member engage with the ratchets when the pawl member is in an operating condition. When the gripped tool handle needs to be released, the pawls should disengage from the ratchets completely in advance.
Chinese patent publication CN 2059607 discloses a chuck capable of moving jaws speedily and used as an accessory of a lathe, wherein the structure of the chuck includes jaws, chuck screw, a chuck body, a bevel gear, a medi wheel axle, a medi-gear and an inner ring gear, etc., and the outer edge of the chuck screw shaped a cylinder gear. The chuck keeps the function of the existing chuck of moving the jaws slowly and additionally has the function of moving the jaws speedily.
Chinese patent publication CN 2671723 discloses a multi functional precision boring head used as an accessory of a lathe, and its structure is as follows: a boring head body being provided on the bottom portion of an spindle, a slider being mounted in a chute below the boring head body, a deceleration transmission mechanism being provided in the boring head body, a differential ring gear being, against the step of the spindle, fitted around the spindle idly, the inner ring gear of the differential ring gear engaging with the upper part of a planet gear while the lower part of the planet gear engaging with the upper part of the inner ring gear of an adjusting ring, the adjusting ring having modulus internal thread at the lower part and engaging with one gear; and this gear drives another gear which engages with a rack below the latter, and the rack being fixed with the slider as one piece. Such a multi functional precision boring head structure, as mounted on a milling machine and a drilling machine, can implement both the boring and processing of an end face of a work piece.
Chinese patent publication CN 2480087 discloses a locking drill chuck, comprising a drill body, jaws, a nut, a front sleeve, and a rear sleeve. Three jaws are mounted respectively in three inclined holes arranged equally in the drill body, the nut engages with the jaws mounted in the inclined holes of the drill body, a locking control ring is provided between the front and rear sleeves, a gear is provided between the thrust surface of the drill body and the nut, and a ring drive member is fixedly connected between the nut and the front sleeve and engages with the locking control ring.
Chinese patent publication CN 1575921 discloses a device for positioning a tool with respect to a work piece, comprising a first bracket rotatable about a first axis and a second bracket rotatable about a second axis formed by the first bracket and carried by the first bracket. The second axis is parallel with the first axis and forms an eccentricity relationship with respect to the first axis. The tool seat is fixed on the second bracket in an eccentricity relationship with respect to the second axis. A drive mechanism selectively drives, in a rotary form, the first bracket about the first axis and the second bracket about the second axis, so as to selectively position the chuck for tools. Along a predetermined path, a tool secured in the chuck for tools may move with respect to the work piece.
Chinese patent publication CN1053206 discloses a keyless chuck of a non-impact type applicable to manual and electrical drivers, comprising a chuck body with a rotatable bisect nut which has relatively fine thread thereon. The chuck further comprises a set of identical slideable jaws driven by the rotatable nut. An anti-friction bearing is provided between a bearing thrust ring and the rotatable nut mounted on the chuck body. A clutch or a torque limit mechanism is used for limiting the gripping torque at a predetermined value and the releasing torque may or may not be limited. The from and rear sleeves may be made of engineering plastic materials to reduce manufacturing cost. A relatively soft elastic gripping sleeve may be provided over the front sleeve to improve the gripping performance during the gripping and releasing of the chuck and have the tool griped and centered temporarily.
A chuck or a similar gripping device has been improved in many aspects by the above-mentioned prior arts and obtained the corresponding effects. However, all of the above chucks and gripping devices perform the gripping in only one way, such that it is difficult to obtain greater gripping force. In addition, those chucks in prior art also have such problems as the locking is not reliable enough and the structure is relatively complicated.